Typically, sleeve-like labels or shrink-sleeve labels are made of polymeric material such as polyethylene terephthalate (PET), polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS) or other materials adapted to be heat-shrunk.
The term “sleeve-like label” or “shrink-sleeve label” designates tubular labels made of plastic film that are designed to be fitted around a respective container to be labeled and subsequently heated, so that the labels shrink onto the external surface of the container and take the shape of the external surface of such container.
Sleeve-like labels are usually obtained starting from a film made of heat-shrink plastic material that is unwound from a spool in order to be fed, by means of a movement device, to a transfer drum.
A cutting device thus performs the cutting of the plastic film transversely to the approach direction, so as to obtain portions of plastic film that have a preset length according to the dimensions of the container to be labeled.
By means of the transfer drum, the portions of film are transferred generally to a carousel, which is provided with devices for forming and transferring the sleeve-like labels to a container to be labeled.
These forming and transferring devices are constituted by respective forming spindles, suitably arranged on the periphery of such carousel and shaped to receive from the transfer drum portions of plastic film so as to obtain respective tubular sleeve-like elements.
A locking head protrudes downward from the lower end of the forming spindle and is designed, during the step of transferring the sleeve-like label from the forming spindle to the container to be labeled, to engage the top portion, generally constituted by the closure, of the container to be labeled in order to keep the latter stably anchored to the pan and in order to allow any angular movement of the container to be labeled about a vertical axis.
The locking head can move on command, along a vertical direction, to alternate between a raised disengagement condition, which is adapted to allow, during the step for feeding the containers to be labeled to the carousel, the arrangement of the container to be labeled in a position below the respective forming spindle and, during the step for unloading the containers from the carousel, the transfer of the container from the pan to the unloading belt, and a lowered engagement condition, in which the locking head presses against the top portion of the container to be labeled.
More precisely, each spindle comprises an external cylindrical wall that has a specific diameter, substantially equal to the preset diameter of the label to be provided, and on which each portion of plastic film is wrapped so that a first longitudinal edge of the portion of plastic film is partially superimposed on the opposite edge of the same portion in an overlap region, so as to form the tubular sleeve-like element.
In the overlap region, the junction is usually provided by using suitable welding techniques so as to obtain a sleeve-like label.
Advantageously, each spindle can be provided with sealing means arranged so as to make the corresponding portion of plastic film adhere to the cylindrical wall and wrap around it.
By way of example, these sealing means may be constituted by a plurality of holes, provided in the cylindrical wall, through which air is drawn from the outside toward the inside of the spindle.
Each spindle, moreover, can be provided with means for expelling air which are designated to facilitate the separation of the sleeve-like label from the spindle itself, so as to expand the spindle radially once the joining operations have been completed.
Each spindle, as mentioned, is generally associated with a support, typically a pan, which is adapted to receive in resting contact a container to be labeled.
Specifically, the sleeve-like label can be fitted onto the container to be labeled by means of a relative axial movement between the label and the container along the longitudinal axis of the latter, so that the sleeve-like label is fitted onto the container.
This operation is normally performed by keeping the container stationary and pushing, for example by means of a pusher, the sleeve-like label from above in order to fit it around the container to be labeled.
The container and the shrink-sleeve label fitted thereon are then guided toward a heating station, in which the label is subjected to a thermal treatment such as to cause its shrinking by thermal effect and, thus, its tight adhesion to the lateral surface of the respective container.
One drawback of the devices for forming and transferring sleeve-like labels currently used consists in the fact that during the step for transferring the label from the forming spindle to the container to be labeled, the label is not “guided” sufficiently by the forming spindle.
In particular, this drawback appears mostly in the case of labels with a considerable vertical extension when the container to be labeled is particularly shaped and therefore is unable, with its lateral surface, to guide the label during descent, and in the case of labels of reduced height, because in this case guiding is ensured almost exclusively by the forming spindle.
This causes, mainly in the case of labeling containers that have significant variations in transverse cross-section along their vertical extension, a risk of label jamming due to possible inclination with respect to the vertical of the label to be transferred.
This causes a certain number of rejects due to an incorrect fitting of the sleeve-like label around the container to be labeled.